Field of the Invention
The present invention relates to an image pickup apparatus including an infrared light reduction section that can be inserted into and removed from an optical path of a photographic optical system, a method of controlling the same, and a storage medium, and more particularly to an image pickup apparatus that inserts or removes the infrared light reduction section according to the luminance of an object.
Description of the Related Art
Conventionally, an image pickup apparatus, such as a digital camera, employs a method of selectively inserting or removing an infrared cut filter which is an infrared light reduction section into or from an optical path of a photographic optical system according to the luminance of an object, and switching a photographing mode (hereinafter referred to as the automatic day/night function).
In the automatic day/night function, when the luminance of an object is higher than a predetermined luminance, near infrared light (having a wavelength of approximately 700 nm or more) is cut by inserting the infrared cut filter into the optical path. On the other hand, when the luminance of an object becomes not higher than the predetermined luminance, the infrared cut filter is removed from the optical path to thereby allow light in the near infrared region to pass and increase the sensitivity.
As described above, if light in the near infrared region is allowed to pass, the color balance of an image is lost, and hence when the infrared cut filter is removed, it is necessary to switch the photographing mode from a color image mode (day mode) to a monochrome image mode (night mode).
Note that the luminance of an object is detected, for example, based on an image signal which is output from an image pickup device, such as a CMOS image sensor, or using a luminance sensor provided separately from the photographic optical system. In a case where the luminance of an object is detected using the luminance sensor, if a photographing range through the photographic optical system and a range of luminance detection by the luminance sensor are different, the luminance of an object is not accurately detected, which makes it impossible to properly switch the photographing mode.
To cope with this problem, for example, there has been proposed a method of correcting the range of luminance detection according to a change in the angle of view of a zoom lens provided in the image pickup optical system to thereby accurately detect the luminance of an object and stabilize switching of the photographing mode (see Japanese Patent Laid-Open Publication No. 2010-279061 and Japanese Patent Laid-Open Publication No. 2007-49442).
However, in the methods described in Japanese Patent Laid-Open Publication No. 2010-279061 and Japanese Patent Laid-Open Publication No. 2007-49442, if the infrared light reflectivity is not uniform in the photographing range through the photographic optical system, an error occurs in correction of the range of luminance detection. Therefore, for example, in a photographing environment in which an object is illuminated with infrared illumination, the infrared light reflectivity is nonuniform in the photographing range through the photographic optical system due to the influence of an object distance or the like, and as a result, it is impossible to stably switch the photographing mode.
Further, there has been proposed an image pickup apparatus that includes an infrared illumination section and illuminates an object with infrared light using the infrared illumination section when in the night mode. This image pickup apparatus positively photographs an object even under low luminance by illuminating the object with infrared light (see Japanese Patent Laid-Open Publication No. 2004-229034).
Incidentally, when the photographing mode is switched based on the object luminance obtained according to the image signal output from the image pickup device, the signal level of the image signal largely varies between a day mode and a night mode. This causes a so-called hunting phenomenon in which the photographing mode is repeatedly switched within a short time.
To prevent the hunting phenomenon, it is envisaged to switch the photographing mode to the day mode in a case where the object luminance becomes higher than an object luminance obtained after switching the photographing mode to the night mode. However, in the image pickup apparatus including the infrared illumination section, if the intensity of light emission by the infrared illumination section changes, it is difficult to switch the photographing mode at a desired timing.
On the other hand, in the image pickup apparatus described in Japanese Patent Laid-Open Publication No. 2004-229034, although the luminance of an object is detected using the luminance sensor provided separately from the photographic optical system, the image pickup apparatus is required to be additionally provided with the luminance sensor, which inevitably increases the costs of the image pickup apparatus itself.